A series of novel, synthetic porphyrin complexes are being prepared and structurally characterized as functional models for several important heme systems: hemoglobin, myoglobin, cytochrome P-450, and cytochromec oxidase. This chemistry has led to a novel series of biomimetic oxygenation catalysts which exhibit shape-selectivity and chiral oxygenation. These are being examined for the preparation of chiral natural products, including terpenes and steroids. A series of myoglobin mimics are being prepared, structurally characterized and the thermodynamic/kinetic parameters for dioxygen binding are being measured. A new series of macrocycle/porphyrin sandwich compounds has been prepared and their iron derivatives have been analyzed in the context of their reversible binding of dioxygen and carbon monoxide. These substances show unprecedented low values of binding but normal values (myoglobin-like) for dioxygen binding. A synthetic analogue for the oxygen binding/activating site in cytochromec oxidase has been prepared. This consists of a macrocycle containing copper positioned over an iron porphyrin which has an axial imidazole bound on the opposite side. This complex binds dioxygen to form a peroxide.